1. Field of the Invention
The present invention relates to an apparatus for carrying on simultaneous signal transmissions over a single optical fiber by using two different operating frequencies, and more specifically to an apparatus for combining bidirectional telephone signals and cable TV signals carried by optical fibers on a single optical fiber extending from a distribution cabinet to a multiplicity of user stations or first locations. The apparatus includes optical couplers for combining the telephone signals and the TV signals onto a single fiber and support and guide structure for organizing a multiplicity of such coupler and input and output fibers for easy access.
2. Description of Related Art Including Information Disclosed Under 37 CFR 1.97 and 1.98
The telecommunications industry is using more and more optical or light fibers in lieu of copper wire. Optical fibers have an extremely high bandwidth thereby allowing significantly more information than can be carried by a copper wire.
Of course, modem telephone systems require bidirectional communications where each station on a communication channel can both transmit and receive. This is true, of course, whether using electrical wiring or optical fibers as the transmission medium. Early telephone communication systems solved this need by simply providing separate copper wires for carrying the communications in each direction. Some early attempts at using optical fibers as a transmission medium followed this example and also used two different optical fibers such as optical fibers 10 and 10A in the prior art FIG. 1 for carrying the communications in each direction. As shown, in the prior art FIG. 1, fiber 10 is connected by an optical coupler 12 to an LED (light-emitting diode) 14 at one end and by optical coupler 16 to a PD (photodetection diode) 18 at the other end. Similarly, but in reverse, fiber 10A is connected by an optical coupler 16A to PD 18A at one end and by optical coupler 12A to LED 14A at the other end.
However, because of extremely high bandwidths available for use by an optical fiber, a single fiber is quite capable of carrying communications in both directions. One technique is WDM (wavelength divisional multiplexing) which is shown in the prior art FIG. 2 and uses different wavelenghts for each direction of travel. Components in FIG. 2 and subsequent figures which operate the same as shown in FIG. 1 carry the same reference numbers. In the embodiment shown in FIG. 2, a central office 20 is connected to an RT (remote terminal) 22 by a single optical fiber 10B. As shown, the central office includes a light-emitting diode 14 optically connected to fiber optics 10 by optical coupler 12 for converting electrical signals to optical signals and a photodetection diode 18 optically connected to optical fiber 10A by a coupler 16 for converting optical signals to electrical signals. The fiber optics 10 and fiber optics 10A are each connected to a wavelength division multiplexer 24 which is connected to optical fiber 10B. This arrangement is duplicated at the RT 22 by light-emitting diode 14A, coupler 12A, photodetection diode 18A, coupler 16A and wavelength division multiplexer 24A. It will, of course, be appreciated that although the figure is shown as providing communications between a central office 20 (station 1) and a remote terminal 22 (station 2), the communications system could be used for providing communications between any two types of stations such as, for example, two central offices, two remote terminal offices, or between a remote office and an individual user""s location, etc. A typical communications system using an LED and a PD with a single optical fiber is disclosed in U.S. Pat. No. 5,075,791 entitled xe2x80x9cMethod and Apparatus for Achieving Two-Way Long-Range Communication Over an Optical Fiberxe2x80x9d, issued to Mark W. Hastings, and incorporated in its entirety hereby by reference.
Yet another and simpler technique for using a single optical fiber 10C for telephone systems is illustrated in the prior art FIG. 3. The illustrated figure is referred to as TCM (time compression multiplexing) and is sometimes referred to as a xe2x80x9cping-pongxe2x80x9d system. The system operates at a single frequency and uses a single optical fiber 10 and a single diode 30 and 30A at each end connected by optical couplers 32 and 32A, respectively, for both converting electrical signals to optical signals and for receiving optical signals and converting those optical signals to electrical signals. TCM systems have the obvious advantage of requiring fewer components.
However, as mentioned above, optical fibers have extremely high bandwidths and use of an optical fiber for a single ping-pong telephone channel is a very ineffective use of the fiber and, in fact, the available bandwidth of an optical fiber makes it possible to use a transmission technique such as TCM or ping-pong at one frequency and then by the use of WDM technology to use another technique at a second frequency. Of course, where optical transmission systems such as a ping-pong or TCM system has been installed, it would not be desirable to disrupt the operation of such systems. Further, once a ping-pong fiber-optic telephone system is installed, removal and replacement with a new system would normally be prohibitive from a cost point of view. Therefore, it would be advantageous to be able to upgrade the existing TCM or ping-pong fiber-optic telephone system to also carry a second communication channel at another frequency.
It is an object of this invention to provide apparatus for upgrading a communication transmission system initially providing a communication channel operating at one frequency so that it can provide two communication channels operating at different frequencies.
It is another object of the invention to provide a method and apparatus to upgrade a communication transmission system while using as much of the existing telephone equipment and distribution frames as possible.
It is still another object of the invention to provide methods and apparatus to upgrade a fiber optic telephone transmission system to carry CATV signals with minimal addition of new components.
It is yet another object of the invention to allow upgrading of a optical fiber communication transmission system to occur on an on-demand-basis.
The present invention accomplishes these and other objects in apparatus for distributing optical transmission which comprises a plurality of first optical fibers which bidirectionally transmit light of a first wavelength. Each one of the plurality of first optical fibers has a first portion spliced to a second portion. There is also included a like or equal number or plurality of second optical fibers for transmitting light at a second wavelength and which, in a preferred embodiment, this second wavelength is used to carry cable TV signals. The plurality of first optical fibers and second optical fibers are provided to a similar plurality or like number of wave division optical couplers (WD) each of which has a first port connected to one of the plurality of first optical fibers and a second port connected to one of the plurality of second optical fibers. Each of the couplers combines light having a first wavelength and which is received from the first plurality of optical fibers at the first port with light having a second wavelength (the TV signals) and which is received from the second plurality of optical fibers at the second port to provide an output at a third port comprised of light carrying both first and second frequencies. The light output at the third port is provided to a similar plurality of third optical fibers which transmit the light at both first and second wavelengths to the user. Each one of the plurality of third optical fibers also has a first portion spliced to a second portion. The invention further includes a support structure or panel which supports the first, second and third plurality of optical fibers and a second enclosed portion which supports the optical couplers. In one embodiment, the apparatus also includes a first holding area for supporting splices joining the first portion and second portions of the first optical fibers and a first pathway which includes support members and guide members which extends from a first external location or port to the first holding area for guiding and supporting the first portions of the plurality of first optical fibers. A second pathway is also included which extends from the first holding area to the enclosed area (preferably by way of an internal port) for guiding and supporting the second portions of the plurality of first optical fibers. Thus, there is provided an organized way for providing optical fibers carrying the first wavelength of light to the enclosed portion of the support structure which houses the plurality of optical wavelength couplers. A second holding area is also provided with support splices joining the first and second portions of the third optical fibers. In a like manner as before, there exists a third pathway extending from a second external location or port to the second holding area for guiding and supporting the first portions of the plurality of third optical fibers and a fourth pathway extending from the second holding area to the enclosed portion of the support structure, such as by a second internal port. This fourth pathway for guiding and supporting the second portions of the plurality of third optical fibers. Thus, it is seen that after combining the first and second wavelengths of light received on the first and second optical fibers and then providing an output on the third optical fiber, the third optical fiber is routed back to the second holding area where it is spliced to the second portion of the third optical fibers and then provided to an external location or port where it leaves the panel.
Also in a preferred embodiment, a small number of fiber optical cables or even a single optical cable carrying the cable TV signals may be provided to the distribution panel of the present invention. In such an event, it will be necessary that the optical fiber carrying the TV signals be split as necessary to provide the same number of outputs of TV signals on second optical fibers as the plurality of first optical fibers. Thus, the present invention also includes at least one optical splitting device which splits the received TV signals to provide outputs to a plurality of second optical fibers equal to the number of first optical fibers. The splitting devices are also contained and supported by the enclosed portion of the distribution panel.
Although the plurality of first optical fibers may be provided in any suitable manner, one preferred arrangement where the first plurality of first optical fibers is equivalent to 96 fibers is provided by 12 ribbons of optical fibers each of which has 8 fibers for a total of 96 first optical fibers. Likewise the third optical fiber which carries both wavelengths of light according to a preferred embodiment is equally divided into 8 ribbons of 12 optical fibers each so as to also have 96 total fibers.
Another feature of the present invention is to provide a panel which can use the existing main distribution frames (MDF) already in existence and used by telephone distribution companies. Therefore, the apparatus or distribution panels of the present invention have dimensions and include brackets such that they can be mounted either vertically or horizontally in a standard telephone main distribution frame. It will also be appreciated, that the present panels can also be mounted in a typical vertical distribution frame used to house optical fibers.
The apparatus according to the present invention comprises a multiplicity of optical couplers or combining units which combine the optical signals carrying information on the first and second optical fibers to produce an output on a single optical fiber which carries the bidirectional telephone signals and the TV signals at different frequencies. Therefore, each one of the plurality of combining units is connected to one of the first optical fibers carrying the bidirectional telephone information at a first frequency, and one of the second optical fibers carrying information at a second frequency. From each combining unit, there is provided a third optical fiber carrying information at both the first and second frequencies. These combining units are mounted in a first enclosed portion of the distribution apparatus.